In the title compound, C7H12N2OS, the 2-sulfanylideneimidazolidin-4-one moiety is nearly planar, with a maximum deviation of 0.054 (2) Å. In the crystal, a pair of N—H⋯O hydrogen bonds and a pair of N—H⋯S hydrogen bonds each form a centrosymmetric ring with an R22(8) graph-set motif. The enanti­omeric R and S mol­ecules are alternately linked into a tape along [1-10] via these pairs of hydrogen bonds.

2-Sulfanylideneimidazolidin-4-one (2-thiohydantoin) derivatives are useful synthetic intermediates with a wide range of applications, such as therapeutics, fungicides and herbicides (Marton et al., 1993). Furthermore, 2-sulfanylideneimidazolidin-4-ones have an interesting structural feature. These compounds commonly carry a thioamide and an amide group in a molecule, which provide equal numbers of the proton donor (D) and the acceptor (A) in a D–A–D–A sequence. Because of this unique structural feature, 2-sulfanylideneimidazolidin-4-ones are expected to form intricate hydrogen bonding networks in crystals. We have been studying the polymorphism and molecular conformations of 2-sulfanylideneimidazolidin-4-one (Ogawa et al., 2009) and their derivatives. In this paper, we report on the crystal structure of the title compound, C7H12N2OS.

In the title molecule (Fig. 1), the 2-sulfanylideneimidazolidin-4-one moiety (S1/O1/N1/N2/C1–C3) is nearly planar, with a maximum deviation of 0.054 (2) Å for atom N2. The N1—C1 distance [1.328 (3) Å] is shorter than the N2—C1 distance [1.389 (3) Å], and the S1—C1—N1 angle [128.62 (17)°] is greater than the S1—C1—N2 angle [124.27 (16)°]. These structural features are similar to those observed in 2-thiohydantoin (Devillanova et al., 1987; Ogawa et al., 2009; Walker et al., 1969) and other 2-thiohydantoin derivatives reported in the Cambridge Structural Database (Version 5.34; Allen, 2002) with both unsubstituted NH groups and sp3-hybridization at C3.

In the crystal structure (Fig. 2), the enantiomeric R- and S-molecules are connected via intermoleculer N1—H1···S1 hydrogen bonds of the neighboring thioamide moieties to form centrosymmetric R22(8) rings (Etter et al., 1990) (Table 1). Furthermore, the other centrosymmetric R22(8) rings are formed via intermolecular N2—H2···O1 hydrogen bonds of the neighboring amide moieties (Table 1). These two different rings are linked alternately into infinite one-dimensional tapes.

The title compound was synthesized by slight modification of a reported method (Wang et al., 2006). A mixture of α-methyl-DL-valine (0.20 g, 1.53 mmol) and thiourea (0.35 g, 4.57 mmol) were allowed to react directly in the absence of any solvent at 180 °C for 5 h. The crude products were further purified by flash column chromatography using hexane and ethyl acetate as eluents (yield: 60%). Colorless crystals suitable for X-ray diffraction analysis were grown by slow evaporation from an aqueous solution.

H atoms bonded to N atoms were located in a difference map and refined freely [N1—H1 = 0.78 (3); N2—H2 = 0.91 (4)]. The remaining H atoms were positioned geometrically (C—H = 0.98 or 1.00 Å) and refined using a riding model, with Uiso(H) = 1.2Ueq(C). A rotating group model was applied to the methyl groups.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F2. R-factor (gt) are based on F. The threshold expression of F2 > 2.0 σ(F2) is used only for calculating R-factor (gt).

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